Direct visualization of current-induced spin accumulation in topological insulators

Yang Liu,Nikesh Koirala,Mengji Chen,Jisoo Moon,Jean Besbas,Seongshik Oh,Yi Wang,Yang Wu,Pan He,Jong Min Lee,Lan Wang,Hyunsoo Yang,Dapeng Zhu

doi:10.1038/s41467-018-04939-6

Abstract

Charge-to-spin conversion in various materials is the key for the fundamental understanding of spin-orbitronics and efficient magnetization manipulation. Here we report the direct spatial imaging of current-induced spin accumulation at the channel edges of Bi2Se3 and BiSbTeSe2 topological insulators as well as Pt by a scanning photovoltage microscope at room temperature. The spin polarization is along the out-of-plane direction with opposite signs for the two channel edges. The accumulated spin direction reverses sign upon changing the current direction and the detected spin signal shows a linear dependence on the magnitude of currents, indicating that our observed phenomena are current-induced effects. The spin Hall angle of Bi2Se3, BiSbTeSe2, and Pt is determined to be 0.0085, 0.0616, and 0.0085, respectively. Our results open up the possibility of optically detecting the current-induced spin accumulations, and thus point towards a better understanding of the interaction between spins and circularly polarized light.

Highlights

Charge-to-spin conversion in various materials is the key for the fundamental understanding of spin-orbitronics and efficient magnetization manipulation
To investigate the effects of the laser helicity on the photovoltage generation, a photoelastic modulator (PEM) acting as a rotating quarter wave plate at a frequency of fPEM ≈ 50 kHz is used to modulate the helicity of light
By employing PEM, a helicity-independent background signal due to the thermoelectric effect in topological insulator (TI) can be substantially suppressed in our helicity-dependent photovoltages (HDPs) measurements

Summary

Introduction

Charge-to-spin conversion in various materials is the key for the fundamental understanding of spin-orbitronics and efficient magnetization manipulation. The interaction between the current-induced spin accumulation with circularly polarized light is less studied especially involving the direct visualization of current-induced spin accumulation in TIs. The spin-to-charge interconversion in TIs has been extensively studied based on ferromagnet (FM)/TI bilayer structures where the FM layer can be used as either a spin injector or detector[35,36,37,38,39,40]. Our work opens up a possibility of optically detecting the accumulated spins in various metallic and semiconducting materials, and helps to extract spin-related parameters such as the spin Hall angle and spin lifetime, propelling a better understanding of the interactions between spins and light in various materials systems

Methods

Results

Conclusion